Goodwill and Other Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2025

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of intangible assets and goodwill

The following table presents the economic life, acquisition date fair value, accumulated amortization and net carrying value for goodwill and other intangible assets as of December 31, 2025 and 2024:

$ in Millions	Weighted Average Economic  Life (in years)	December 31, 2025								December 31, 2024
		Acquisition Date Fair Value		Accumulated Amortization		Impairments (3)		Net Carrying Value		Acquisition Date Fair Value		Accumulated Amortization		Net Carrying Value
Goodwill:
Ark	N/A	$	116.8	$	—	$	—	$	116.8	$	116.8	$	—	$	116.8
Kudu	N/A	7.6		—		—		7.6		7.6		—		7.6
Bamboo (1)	N/A	—		—		—		—		270.4		—		270.4
Distinguished (2)	N/A	396.7		—		—		396.7		—		—		—
Other Operations	N/A	102.1		—		9.1		93.0		44.4		—		44.4
Total goodwill		623.2		—		9.1		614.1		439.2		—		439.2
Other intangible assets:
Ark
Underwriting capacity	N/A	175.7		—		—		175.7		175.7		—		175.7
Kudu
Trade names	7.0	2.2		2.1		—		.1		2.2		1.8		.4
Bamboo (1)
Trade names	N/A	—		—		—		—		23.5		2.3		21.2
Agency relationships	N/A	—		—		—		—		72.4		12.1		60.3
Developed technology	N/A	—		—		—		—		4.7		1.6		3.1
Other	N/A	—		—		—		—		.4		.4		—
Subtotal		—		—		—		—		101.0		16.4		84.6
Distinguished (2)
Trade names	10.0	24.3		.8		—		23.5		—		—		—
Agency relationships	8.0	127.9		2.0		—		125.9		—		—		—
Developed technology	5.0	36.6		5.0		—		31.6		—		—		—
Subtotal		188.8		7.8		—		181.0		—		—		—
Other Operations (2)
Trade names	11.7	22.4		7.7		.2		14.5		13.3		5.6		7.7
Customer relationships	8.8	53.3		19.4		.3		33.6		24.8		13.6		11.2
Other	11.8	3.1		1.9		—		1.2		3.1		1.6		1.5
Subtotal		78.8		29.0		.5		49.3		41.2		20.8		20.4
Total other intangible assets		445.5		38.9		.5		406.1		320.1		39.0		281.1
Total goodwill and other intangible assets		$	1,068.7	$	38.9	$	9.6	$	1,020.2	$	759.3	$	39.0	$	720.3

(1) Goodwill and other intangible assets associated with Bamboo were disposed of in connection with the Bamboo Sale Transaction. See Note 2 — “Significant Transactions.”

(2) The relative fair values of goodwill and other intangible assets recognized in connection with the Distinguished Transaction and the Enterprise Solutions Transaction have not yet been finalized. See Note 2 — “Significant Transactions.”

(3) Impairment is related to an Other Operating Business.

The following table presents the change in goodwill and other intangible assets for the years ended December 31, 2025 and 2024:

	December 31, 2025						December 31, 2024
Millions	Goodwill		Other Intangible Assets		Total Goodwill and Other Intangible Assets		Goodwill		Other Intangible Assets		Total Goodwill and Other Intangible Assets
Beginning balance	$	439.2	$	281.1	$	720.3	$	168.8	$	201.8	$	370.6
Acquisitions of businesses (1)	690.8		—		690.8		270.4		101.0		371.4
Acquisitions of intangible assets (2)	—		—		—		—		.3		.3
Measurement period adjustments (3)	23.1		—		23.1		—		—		—
Attribution of acquisition date fair value estimates    between goodwill and other intangible assets (1)	(235.6)		235.6		—		—		—		—
Amortization	—		(28.4)		(28.4)		—		(22.0)		(22.0)
Impairments (4)	(9.1)		(.5)		(9.6)		—		—		—
Dispositions (5)	(294.3)		(81.7)		(376.0)		—		—		—
Ending balance	$	614.1	$	406.1	$	1,020.2	$	439.2	$	281.1	$	720.3

(1) During 2025, amounts relate to the Distinguished Transaction and the Enterprise Solutions Transaction. The relative fair values of goodwill and other intangible assets recognized in connection with the Distinguished Transaction and the Enterprise Solutions Transaction have not yet been finalized. During 2024, amounts relate to the acquisition of Bamboo. See Note 2 — “Significant Transactions.”

(2) Relates to acquisitions within Other Operations.

(3) Measurement period adjustments relate to updated information about acquisition date fair values of assets acquired and liabilities assumed. Adjustments relate to the Distinguished Transaction and the Enterprise Solutions Transaction.

(4) Impairment is related to an Other Operating Business.

(5) Relates to the Bamboo Sale Transaction and the sale of a small, non-core ScaleCo program at Distinguished. See Note 2 — “Significant Transactions.”

Schedule of finite-lived intangible assets, future amortization expense

The following table presents a schedule of White Mountains’s future amortization expense as of December 31, 2025:

Millions	Amortization Expense
2026	$	35.5
2027	34.1
2028	33.2
2029	32.8
2030	29.3
2031 and years after	65.5
Total (1)	$	230.4

(1) Excludes Ark’s indefinite-lived intangible assets of $175.7.